Conventional automobile powertrains require thermal management to make the most efficient use of the thermal energy therein. Most vehicles include a heater core in thermal communication with a vehicle engine. A transmission fluid warmer can be used to add heat to the transmission particularly when starting the vehicle or operating in park or lower gears. In some instances, the transmission fluid warmer can receive thermal energy from the engine through coolant circulated through the heater core. In doing so, heating of the transmission fluid is expedited.
Faster automatic transmission fluid warming is desirable to improve fuel economy. Pulling heat from the cooling circuit to heat the transmission fluid can lead to problems. One problem created by this method is that heater performance can be negatively impacted. To reduce such impact on heater performance, a bypass valve can be installed to selectively avoid flowing fluid through the automatic transmission fluid warmer. The bypass valve can be used when heater performance is a priority and turned off when fuel economy is a priority. When considering the trade-offs made in controlling the valve, designing the valve controls can be particularly nuanced.
One existing design includes the use of a vehicular lockup clutch-equipped transmission control apparatus which is described as reducing deterioration of heating capability and improving fuel efficiency. U.S. Pat. No. 6,695,743 titled “Vehicular lockup clutch-equipped transmission control apparatus and control method thereof” discloses a flow control valve that is controlled by the engine control unit. In response to various temperature readings, the system sets the lockup region for the clutch to provide a desired fuel economy and heating capability. While these types of systems can improve fuel efficiency they can also heat the transmission fluid during unwanted periods of time and direct heat away from the engine at undesirable points.
Therefore, it is desirable to have a thermal management system for a vehicle powertrain with improved thermal management and fuel efficiency.